Effects of field dependent relaxation time on x-space MPI images

In magnetic particle imaging (MPI), nanoparticle relaxation delays the response of the super paramagnetic iron oxide nanoparticles (SPIO) magnetization to the applied magnetic field. Relaxation can be a significant issue in MPI, since the delayed response can deteriorate the quality of MPI images: due to relaxation, both the resolution and the signal-to-noise ratio (SNR) of the MPI images will worsen. Previously, the SPIO relaxation effect in MPI was modeled as a single time constant using the first-order Debye relaxation process. While this model provided a good fit to the experimental data, it does not capture the full response of the SPIOs: instantaneous magnitude of the sinusoidal drive field is time-varying, which in turn will cause the relaxation time to vary. In this work, the effects of field dependent relaxation time on MPI images reconstructed with the x-space technique are presented.